The long-term objective of this program is the extended low temperature preservation of organs and, by extension, of vascularized tissues in general. A critical component of the program has been and will continue to be basic studies to elucidate further the mechanisms of freezing injury and of cryopreservation. The proposed basic studies are directed in part at the nature of cell membrane injury from osmotic dehydration and in part at an exploration of naturally acquired mechanisms of freezing tolerance. A polymer synthesised by poplar cells during winter hardening which is capable of suppressing ice formation below -20 C will be isolated and characterized. Applied studies of organ cryopreservation have led to the development of a procedure by which ice formation can be totally prevented (vitrification) by using a combination of cryoprotective agents and hyrostatic pressusre. This approach to cryopreservation is so promising that studies now being proposed will focus exclusively on the development of this technique. Vitrifiable additive solutions that are non-toxic for rabbit kidney slices have been developed and will be tested in samll mammal organs. If these experiments are successful, the procedure will be scaled up to permit studies with dog kidneys. If rewarming can be sufficiently rapid, pressurizing the specimen to prevent devitrification will be unnecessary. The use of microwave heating for this purpose will be explored. Since vitrification entirely obviatesmost of the problems associated with freezing, this new approach to low temperature preservationcan have broad applicability.